Method and device for determining the swelling behavior of polymer gels under pressure

ABSTRACT

Disclosed is a method for determining the swellability and the swelling kinetics of superabsorbent material ( 9 ) such as polymer gels, for example, which comprises introducing a defined volume of the dry superabsorbent material ( 9 ) into a measuring vessel ( 7 ), using a movable element ( 4 ) within said measuring vessel ( 7 ) to apply a restraining force ( 12 ) to said superabsorbent material ( 9 ) and capturing the expansion of said superabsorbent material ( 9 ) contactlessly within a chamber ( 14 ) in a continuous manner by capturing the change in height of a piston ( 4 ) which bounds said chamber ( 14 ), travels in a measuring vessel ( 7 ) and is marked with a height scale ( 6 ).

[0001] This invention relates to a method and apparatus for determiningthe swellability under load of polymer gels, especially lightlycrosslinked polymer gels formed from acrylic acid, salts of acrylic acidand acrylates.

[0002] Lightly crosslinked polymer gels, which are preferably preparedform acrylic acid, salts of acrylic acid, acrylates and bifunctionalcrosslinkers, are capable of imbibing, absorbing or gelling a multipleof their own weight (typically up to 100 times their own weight) ofwater or salt-containing fluids via osmotic pressure. An essentialproperty of these superabsorbent gels is that they retain the absorbedfluids even under pressure. The main applications of superabsorbentpolymer gels are in hygiene products, for example infant diapers orincontinence products for adults. These diapers contain superabsorbentpolymer gels as an essential component. Important product properties areFree Swell Capacity (FSC), Centrifuge Retention Capacity (CFC) andAbsorbency Under Load (AUL), and also the rate of absorption.

[0003] Absorption properties, especially FSC and CRC, are currentlydetermined by the teabag method. To this end, a certain amount of thepolymer gel is weighed into a teabag, and the teabag is then sealed andimmersed in a 0.9% sodium chloride solution for 20 minutes. The teabagis then reweighed. The weight of the salt solution which has beenabsorbed, based on the amount of polymer gel used, is termed FSC. If theteabag, after it has been immersed, is centrifuged at about 250 g for 3minutes and then weighed, the second weighing operation yields the CRC.

[0004] As regards the absorbency of polymer gels under load, EP 0 339461 A1 discloses a method for determining the absorbency of the gelunder load. EP 0 339 461 A1 relates to absorbent products comprisinggels with ability to swell against pressure.

[0005] An absorbent material, which constitutes a porous matrix offibers and superabsorbent material, accommodates the superabsorbentmaterial among the interfiber spaces of the porous matrix. Thesuperabsorbent material exhibits the ability to absorb about 24 ml of asaline solution per gram of superabsorbent material under a certainapplied restraining force provided it is in the form of discreteparticles where at least 50% of the superabsorbent material has a sizegreater than the median pore size of the matrix when wet.

[0006] The absorbency of the gel in the porous matrix is determined inEP 0 339 461 A1 by the hereinbelow described method:

[0007] An absorbency tester is used that has a porous plate having amultiplicity of ports which end within the porous plate. The individualports communicate via a conjoint line with the absorption testerreservoir which in turn is disposed on an electro balance. The balanceis used to measure the resulting flow of fluid into hydrocolloidparticles. The colloid particles are contained in a special vessel whichis concentric with regard to a mesh and in which a bottom has beeninserted. A Plexiglass piston is inserted into the vessel and weightedwith a 100 g weight. This applied restraining force is used to simulatethe restraining load which is experienced in infant diapers, forexample. Preselected granules are utilized as superabsorbent materialfor testing the Absorbency Under Load and introduced into the vesselbefore the Plexiglass piston and the weight it is to bear are insertedinto the vessel.

[0008] The test is initiated by placing a filter paper onto the meshstructure above the ports in such a way that undesirable evaporationover the ports is eliminated and saturation is allowed to occur. About0.16 g of particles of the superabsorbent gel is placed on the undersideof the vessel; the filled vessel bearing the piston with its weight ontop is placed on the filter paper. The amount of fluid pick-up ismeasured by hand. The measured values thus obtained are checked twice toexamine the values obtained with regard to plausibility and spuriousmeasurements.

[0009] The disadvantages of the prior art represented by EP 0 339 461 A1are in particular that the test method described is demanding in termsof personnel, since many operations such as weighing and adding polymerand salt solutions, removing and adding filter paper and weighing theswollen gel have to be substantially carried out by hand. Because themeasured results fluctuate moreover, multiple determinations have to becarried out with subsequent averaging. All this militates against highsample throughput. Furthermore, the method described does not permitdetermination of swelling kinetics.

[0010] It is an object of the present invention to provide a method forcontactless determination not only of absorbency under load but also ofswelling kinetics.

[0011] We have found that this object is achieved by a method fordetermining the swellability and the swelling kinetics of superabsorbentmaterial such as polymer gels, for example, which comprises introducinga defined volume of the dry superabsorbent material into a measuringvessel, using a movable element within said measuring vessel to apply arestraining force to said superabsorbent material and capturing theexpansion of said superabsorbent material contactlessly within a chamberin a continuous manner by capturing the change in height of a pistonwhich bounds said chamber, travels in a guide and is marked with aheight scale.

[0012] The method proposed according to the invention makes it possibleto record the kinetics of the swelling process via continuousmeasurements, for example via a CCD optical system, during swelling.Preference is given to carrying out automatic computer-controlledmeasurements which entail only a minimum of costly, manual operationsand so eliminate human factors in the measurement, for example incorrectreading of the height with corresponding impairment of the measurementaccuracy. The method proposed according to the invention providesincreased sample throughput through parallelization of the method.Beneficially a plurality, for example up to 1 000 or particularlypreferably up to 100, tubes can be disposed side by side and/or onebehind the other and/or else wholly or partly one on top of the other sothat one or more, for example optical, observing means can be used toprovide synchronous capture of the heights of rise of the pistons in aplurality of measuring vessels. Owing to the high sample throughput,complicated measurements involving many samples and controlled or randomvariation of the parameters, for example variation of the chemicalcomposition, of the polymerization process, of the ionic strength, ofthe pH and of the degree of neutralization, can be carried out in a veryshort time. The method proposed according to the invention accordinglyprovides faster and less costly product development.

[0013] In a further refinement of the concept underlying the invention,the contactless determination of the height of rise of the measuringpiston provided with a scale may be captured optically in front of abackground area providing a contrast to the chosen scale on the piston.Optical capturing allows freely preselectable time intervals in whichmeasurement can be carried out, so that almost continuous swellingkinetics curves can be recorded.

[0014] In a preferred further development of the method proposedaccording to the invention, the pixel coordinate which corresponds tothe tip of said scale on said pistons is convertible into a swell heightof said superabsorbent material via calibration. The relationshipbetween the pixel coordinate reflecting the height of rise of the pistonand the swell height of the particular superabsorbent material measuredcan be represented in terms of characteristic lines.

[0015] In the method of the invention, suitable dimensioning of thepiston and of the material of the piston can be used to vary therestraining force acting on the superabsorbent material in the measuringvessel. As well as ensuring convenient reproducibility for therestraining forces acting on the superabsorbent material, thisembodiment provides a very convenient way of varying the restrainingforces acting in each case, and of conforming to the various testcycles.

[0016] Preferably, particulate superabsorbent material in particlessizes of from 100 μm to 1 mm, particularly preferably in particle sizesfrom 400 μm to 700 μm, is introduced into the measuring vessel, a sievefabric provided at the underside of the measuring vessel ensuring thatthe particulate superabsorbent material is always kept in contact withan aqueous saline solution in the reservoir into which the lower,glass-fritted region of the measuring vessel dips.

[0017] As well as by contactless capture of height of rise of the scaleon the piston by optical means, for example by use of a CCD camera, theheight of rise of the scale on the piston may be captured by adetermination of the electrical conductivity of the superabsorbentmaterial. As well as electrical conductivity of the superabsorbentmaterial, the capacity of the superabsorbent material may be used todetermine the swellability or swelling kinetics of the superabsorbentmaterial. Furthermore, the expansion behavior and the swelling kineticsof the superabsorbent material may be realized via the determination ofthe mechanical deflection of the superabsorbent material.

[0018] The method of the invention provides an optical way ofcontactlessly determining the swelling kinetics of the superabsorbentmaterial accommodated in the chamber of the measuring vessel bycontinuous, contactless measurement over a time span Δt. During thistime span, swelling kinetics corresponding to the fractions of particlesof the superabsorbent material to be evaluated can be plottedcontinuously on a representational surface, for example a PC screen orother medium, at freely preselectable points in time.

[0019] In a particularly economical way of using the method proposedaccording to the invention, said contactless capturing of said heightsof rise of said scale on pistons is effected concurrently on amultiplicity of parallel-connected measuring vessels which dip into aconjoint reservoir and are synchronously engageable to a saline solutionvia said conjoint reservoir. The simultaneous immersion of the measuringvessel in a conjoint reservoir ensures simultaneous initiation of theprocess of swelling of the particular particulate superabsorbentmaterial accommodated in the measuring vessels. The multiplicity oftube-shaped measuring vessels in a side-by-side arrangement may in apreferred embodiment be associated with a background area whichcorresponds to the widthwise extension of all the measuring vessels andcontrasts with the scales on the pistons. A contactless capture means,for example an optical CCD camera, is movable in such a way that theentire background surface extending over the width of the individualmeasuring vessels accommodated side by side can be scanned. Themultiplicity of the measuring vessels can be arranged side by sideand/or one behind the other and/or wholly or partly one above the other,depending on the geometry of the space available to accommodate themeasuring apparatus.

[0020] For instance, contactless capturing of said height of rise ofsaid scales on said multiplicity of pistons can be effected in staggeredmeasuring planes located one behind the other or one above the other bya movable optical system. Preferably, said vertically movable piston insaid measuring vessel generates pressures >50 Pa on said superabsorbentmaterial.

[0021] The inventive method of using a movable optical system, forexample a CCD optical system, to continuously capture the heights ofrise of the scales on the pistons in front of a contrasting backgroundarea as a function of time is preferably actualizable on an automaticcomputer-aided system of evaluation below the movably disposed opticalsystem. The evaluating system below the optical capturing system may beused to represent swelling kinetics reflecting various parameterizationson different scales on a magnified scale in particularly interestingtransition regions and the like.

[0022] This invention further provides apparatus for determining theswellability or swelling kinetics of superabsorbent material such aspolymer gels, for example, which comprises introducing a defined volumeof the dry superabsorbent material into a measuring vessel, using amovable element within said measuring vessel to apply a restrainingforce on said superabsorbent material, wherein said superabsorbentmaterial is accommodated in a chamber of said measuring vessel and issubjected to a restraining force by a movable piston in the measuringvessel, piston and measuring vessel being constructed in metal, and saidchamber being in communication with a saline solution through a sieveand a frit.

[0023] The advantages provided by apparatus configured according to theinvention are in particular that it is now possible to measure theexpansion of superabsorbent material in a reproducible manner that isindependent of operator effects and that the piston guided movablywithin the measuring vessel makes it possible to exert a definedrestraining force on the superabsorbent material whose expansioncharacteristics or swelling kinetics are to be determined. A metallicconstruction for measuring vessel and piston prevents undesirableelectrostatic charge build-up of the two components which are movablerelative to each other, whereby polymer gel particles could becometrapped between piston and tube and disrupt or completely stop theswelling-based movement of the piston.

[0024] A preferred embodiment of the movable piston is made of ametallic material which has been provided with the scale in the regionof its upper end face. The scale on the upper end face of the movablepiston facilitates the determination of the height of rise of thepiston, especially in front of the background area which contrasts withthe scale. In a preferred embodiment of the apparatus proposed accordingto the invention, the measuring vessels may be positioned as amultiplicity of size-by-side individual measuring vessels in front of acontrasting background area which is common to all measuring vessels andwhich is scanned by an optical system which can be stationary or elsemovable with regard to the measuring vessels. To ensure simultaneouscommencement of swelling in all measuring vessels disposed side by side,the individual measuring vessels are supplied at their underside by areservoir which is common to all measuring vessels and which preferablyaccommodates a saline solution. To speed up sample throughput and toprocess a multiplicity of superabsorbent material samples in parallel, amultiplicity of measuring vessels can be disposed in staggered measuringplanes, in which case the movable pistons of the multiplicity ofmeasuring vessels are, for the purposes of the heights of rise of thepistons being determined, disposed in front of contasting backgroundareas which are each assigned one measuring plane, the contrastingbackground area corresponding to a measuring plane being scannable inits totality by the movable optical system

[0025] The invention will now be more particularly described withreference to the drawing, where

[0026]FIG. 1 shows the construction of a measuring vessel with movablepiston having a scale and bounding a chamber with its bottom end face,

[0027]FIG. 2 shows recorded swelling kinetics of two sieved fractions ofsuperabsorbent material of different particle sizes,

[0028]FIG. 3 shows an arrangement of pistons which are accommodated sideby side and are engaged from a conjoint reservoir containing a salinesolution, and

[0029]FIG. 4 shows a staggered measuring arrangement for contactlessdetermination of the swellability of superabsorbent material by using anoptical system to determine the extension of a metallic piston.

[0030] The representation as per FIG. 1 reveals in more detail theconstruction of a measuring vessel containing a movable piston on whicha scale is marked and whose bottom end face bounds a measuring chamber.

[0031] According to the representation in FIG. 1, a tube-shapedmeasuring vessel 7 may optionally have a contrasting background area 1provided behind it. The contrasting background area I has a sidewayswidth extension 2 and also a vertical height extension 3 and describes aplane behind the tube-shaped measuring vessel 7.

[0032] The apparatus proposed according to the invention may include afurther suitable source of illumination in order that lighting suitablefor measurement may be provided independently of environmentalinfluences. The contrasting background area 1 has the purpose, togetherwith the source of illumination, of creating optimal conditions by meansof an optical system, independently of environmental influences such asroom lightness, daylight, etc.

[0033] The tube-shaped measuring vessel 7, preferably made of metallicmaterial, accommodates on its inside a piston 4, which is likewisefabricated from metallic material. At the upper end in the region of thetop end face 5 of the metallic piston 4 is marked a scale 6 in a colorwhich contrasts with the background area 1. In the depicted illustrativeembodiment of the apparatus configured according to the invention, thescale 6 forms a ring-shaped attachment at the upper end of the metallicpiston 4. By fabricating the tube-shaped measuring vessel 7 and thepiston 4 from metallic material it is possible to avoid the build-up ofundesirable electrostatic charges which could cause gel particles ofsuperabsorbent material 9 to become trapped between the piston 4 and theinside surface of the measuring vessel 7 and to interfere with orcompletely prevent the swelling-based movement of the piston 4 relativeto the surrounding measuring vessel 7.

[0034] A bottom end face 10 of the piston 4 bounds a chamber 14 formedby the inside surface of the measuring vessel 7. The bottom of thechamber 14 is formed by a sieve fabric 13. The sieve fabric 13 issituated above a filter insert 15 surrounded by a solution 17.Underneath the filter insert 15 is a glass frit 16 to ensure that theamount of superabsorbent material 9 accommodated in the measuringchamber 14 is always in contact with the saline soluton accommodated inreservoir 19. This ensures a continuous swelling process of thesuperabsorbent material 9 within the chamber 14. Reference numeral 18identifies the surface of the solution 17 accommodated in vessel 19.

[0035] Depending on the geometric configuration and on the material usedfor the piston 4, a restraining force, identified by reference numeral12, results on the portion of superabsorbent material 9 accommodated inchamber 14. The restraining force 12 is preferably set to a value whichreflects conditions of actual service, i.e., it is possible to simulatethe restraining forces to which a portion of superabsorbent material 9included in an infant diaper for example is subjected in real life. Thechamber 14 is bounded on the side by the inside surface 11 of thepreferably metallic measuring vessel 7, the bottom end face 10 of themetallic piston 4 and the sieve fabric 13 inserted in the bottom of themeasuring vessel 7.

[0036] The apparatus exemplified in FIG. 1 for determining the expansionof a superabsorbent material 9 against a pressure is associated with acontactless capturing means 20 in the shape of a CCD camera. The CCDcamera 20 has a suitable lens 22 whereby continuous measurements can becarried out. As indicated by the double-headed arrow, the stand 21 forthe contactless capturing means 20 is movable relative to the measuringvessels. The contactless capturing means 20 can be used to providecontinuous measurements to determine the kinetics of the swellingprocess during the swelling process. The contactless capturing means 20,for example embodied as a CCD linescan or array camera, can be used tocarry out automatic, computer-controlled measurements which require onlya miniumum of costly manual operations, so that human sources of errorcan be eliminated, for example an inaccurate reading of the height ofrise of the pistons 4 with an associated impairment of the accuracy ofmeasurement. The swelling of the superabsorbent material 9 in thechamber 4 causes the piston 4 to rise. The rise of the piston 4, whichis guided in the measuring vessel 7 so as to be movable in the verticaldirection, leads to a height shift of the scale 6 accommodated at thetop end face 5 of the piston 4 and contrasting with the background area1. The resulting change of height in the scale 6 of the piston 4 iscaptured via the contactless, preferably optical, capturing means 20,which continously records images of the metallic piston 4. Appropriatecalibration makes it possible to convert the pixel coordinate whichcorresponds to the tip of the piston 4 into a swell height of thesuperabsorbent material 9 accommodated in the chamber 14. This makes itpossible to determine the kinetics of the swelling process and theequilibrium swelling volume which is present after a certain time span.

[0037] The inventive method, the basic features of which are moreparticularly depicted with reference to FIG. 1, makes it possible tosubstantially increase sample throughput through parallelization of themeasuring procedure. Preferably, for example, a multiplicity of up to 1000, particularly preferably 100, tube-shaped measuring vessels 7 arearranged side by side and/or one behind the other and/or else wholly orpartly one above the other, so that the heights of rise of the pistons 4in a plurality of measuring vessels 7 can be simultaneously capturedusing one or more optical capturing means 20. A further advantage of themethod proposed according to the invention is that only one or a fewreservoirs 19 of aqueous or saline solution have to be provided and sosimultaneous commencement of the swelling process is ensured. Anautomatic image analyzer below the optical capturing means 20 makes itpossible to determine all heights of rise or rise kinetics of therespective superabsorbent material 9 under various restraining forces12.

[0038] In a preferred procedure, the particulate superabsorbent material9, for example particle sizes of 200 μm, is introduced via a spoonhaving a plurality of identical or different volumes which can beleveled off in one operation. As a result, the chambers 14 within thetube-shaped measuring vessels 7 can each be supplied with identical dryvolumes of the superabsorbent material 9. Measuring accuracy may beincreased by averaging.

[0039] The depiction as per FIG. 2 illustrates two exemplary kinetics oftwo sieve fractions of superabsorbent material of different particlesizes.

[0040] In the depiction as per FIG. 2, reference numeral 23 signifiesthe height of rise of scale 6 on the vertically movable piston 4 in themeasuring vessel 7. Reference numeral 24 identifies the time axis alongwhich the swelling kinetics, here depicted as traces 25 and 26 by way ofexample, may be recorded in arbitrarily preselectable time intervals.Reference numeral 25 identifies for example the swelling kinetics of asieve fraction having a particle size of from 400 to 500 μm, recordedover the time span of about an hour. In contrast, reference numeral 26identifies the swelling kinetics of a second sieve fraction, which has asmaller particle size of only 200 to 300 μm. A comparison of the twokinetic curves shows that the swelling kinetics 25 and 26 of the twosieve fractions result in a rapid rise of the scale 6 on the metallicpiston 4 at the start of the swelling process, whereas the swellingkinetics curves 25 and 26 asymptotically approach a maximum as swellingcontinues. The height of rise of the swelling kinetics as per referencenumber 26 has reached its maximum after 10 minutes and does not changethis maximum any more for the time span of the measurement, whereas inthe case of the swelling kinetics as per reference numeral 25,corresponding to the first sieve fraction of smaller particles of thesuperabsorbent material shows a further merely slightly asymptoticincrease in the height of rise of the piston 4.

[0041] The individual data points are plottable for example as a pixelcoordinate on the contrasting background area 1, so that a trace of theswelling kinetics or of the heights of rise of the individual pistons 4can be generated directly as a function of the restraining force setting12 and of the superabsorbent material 9 used.

[0042] The depiction as per FIG. 3 reveals an arrangement of pistonswhich are accommodated side by side and are engageable by means of acommon reservoir containing saline solution.

[0043] This configuration of the process again includes as contactlesscapturing system 20 a CCD camera whose stand 21 is movable in thedirection of the double-headed arrow, although it also conceivable tohave a stationary stand 21 coupled with an optical system having asuitable depth of field, so that the entire widthwise extension of thebackground area 27 which extends over the width of all pistons 4 ispossible.

[0044] In contrast to the depiction of an individual measuring apparatusas per FIG. 1, the arrangement as per FIG. 3 has a multiplicity 29.1 to29.12 of measuring vessels 7 arranged side by side. Each of themeasuring vessels 7 contains a preferably metallic piston 4 which, inthe region of its upper end face 5, is provided with a scale 6 which isconstructed so as to provide a contrast with the background area 27. Onthe underside of every measuring vessel 7 is a glass frit 16 to ensurethat the portion of superabsorbent material 9 accommodated in thechambers 14 of the respective measuring vessels 7 of the multiplicity29.1 to 29.12 of measuring vessels is always in communication with thesolution medium stock contained in the reservoir 28 which is common toall measuring vessels. This ensures simultaneous commencement ofswelling of the portions of superabsorbent materials each accommodatedin the chambers of the multiplicity 29.1 to 29.12 of the individualmeasuring vessels.

[0045] The depiction as per FIG. 4 more particularly illustrates astaggered measuring arrangement for contactless determination of theswellability or swelling kinetics of superabsorbent materials by meansof a movable optical system which scans the contrasting background areaof the measuring arrangements. Similarly to the depiction as per FIG. 3,there is provided a contactless capturing means 20 which is preferablyembodied as a CCD camera. The stand 21 of the CCD camera 20 can be movedparallel to the background areas 27. The contactless, in this exampleoptical, capturing means 20 accommodates a lens 22 whose focal length isconformable to the position of the individual background areas 27. Inthe arrangement illustrated here there are staggered arrangements ofpistons 4 whose multiplicity 29.1 to 29.12 of individual pistons isengageable via a common solution reservoir 28. Each of the multiplicity29.1 to 29.12 of individual measuring vessels 7 is assigned acontrasting background area 27 which extends across the width of themeasuring arrangement. The individual reservoirs 28, which contain thesaline solution medium, are partly arranged one above the other,resulting in a staggered measuring arrangement. The illustrativeembodiment depicted in FIG. 4 has for example four measuring planes 32,33, 34, 35 connected in series which are evaluable via a singlecontactless capturing system, increasing the sample throughput by afactor of 4 compared to FIG. 3. In the case of the arrangement shownhere in FIG. 4, it is merely necessary to ensure that the optical system22 of the optical, contactless capturing means 20 can be sharply focusedon the image plane and hence on the pixel coordinates which indicate theheight of rise of the individual pistons 4. The staggered arrangement ofthe individual measuring planes is such that not only the respectivemultiplicity 29.1 to 29.12 of the individual measuring vessels in eachof the measuring planes 32, 33, 34 and 35 is assigned a background area27 corresponding to the measuring plane position. The method proposedaccording to the invention and the apparatus configured according to theinvention provide an increase in sample throughput throughparallelization of the process. In the depiction as per FIG. 4, forexample, 50 individual measuring vessels are evaluable via a singlecontactless optical capturing system 20. The method proposed accordingto the invention dramatically improves the reproducibility of themeasurement while at the same time saving manual operations. Owing tothe high sample throughput, complicated measuring series involving manysamples with controlled or random variation of the parameters such as,for example, the chemical composition, the polymerization process, theionic strength, the pH and the degree of neutralization can be carriedout within a shorter time span. An appreciable cost saving is providedas well as a speeding up in the measuring series.

[0046] An individual measurement using an individual measuring vessel 7as per FIG. 1 is effected as follows: a measuring spoon having acapacity of 70 μl is filled with Aqualic Cal 400 superabsorbent granulesand leveled off, leaving a starting weight of 40 mg ±3%. This isintroduced into the tube-shaped measuring vessel. Subsequently, piston 4which at a weight of 39.6 g generates a pressure of 4 900 pascal isinserted. When all cylinders of a parallel measuring arrangement areprepared thus, the reservoirs 19 and 28 are filled with an isotonicsodium chloride solution so that the liquid surface 18 reaches the upperedge of the filter element 15. Thereafter, all tube-shaped measuringvessels 7 are placed on top of the filter element 15 and the measurementis started at the same time. The liquid pick-up of the superabsorbentmaterial 9 accommodated in the chamber 14 is then measured continuallyvia an optical capturing means 20 by having a computer program determinethe height of rise of scale 6 on piston 4. These heights of rise can beconverted by means of characteristic-line relations into the liquidabsorbency of the corresponding superabsorbent material 9 which is to beinvestigated with regard to its absorbency under load and its swellingkinetics.

LIST OF REFERENCE NUMERALS

[0047]1 Background area

[0048]2 Sideways extension

[0049]3 Vertical extension

[0050]4 Piston

[0051]5 Upper piston end face

[0052]6 Scale

[0053]7 Measuring vessel

[0054]8 Guide upper edge

[0055]9 Superabsorbent material

[0056]10 Bottom end face

[0057]11 Cylinder wall

[0058]12 Restraining force

[0059]13 Sieve fabric

[0060]14 Chamber

[0061]15 Filter element

[0062]16 Glass frit

[0063]17 Solution

[0064]18 Liquid level

[0065]19 Reservoir

[0066]20 Capturing means

[0067]21 Stand

[0068]22 Lens

[0069]23 Piston scale height of rise

[0070]24 Time axis

[0071]25 Swelling kinetics of 1st sieve fraction

[0072]26 Swelling kinetics of 2nd sieve fraction

[0073]27 Continuous background area

[0074]28 Conjoint solution reservoir

[0075]29.1 Measuring vessel

[0076]29.2 Measuring vessel

[0077]29.3 Measuring vessel

[0078]29.4 Measuring vessel

[0079]29.5 Measuring vessel

[0080]29.6 Measuring vessel

[0081]29.7 Measuring vessel

[0082]29.8 Measuring vessel

[0083]29.9 Measuring vessel

[0084]29.10 Measuring vessel

[0085]29.11 Measuring vessel

[0086]29.12 Measuring vessel

[0087]30 Staggered arrangement of pistons

[0088]31 Staggered arrangement of background areas

[0089]32 1st measuring plane

[0090]33 2nd measuring plane

[0091]34 3rd measuring plane

[0092]35 4th measuring plane

We claim:
 1. A method for determining the swellability and the swellingkinetics of superabsorbent material (9) such as polymer gels, forexample, which comprises introducing a defined volume of the drysuperabsorbent material (9) into a measuring vessel (7), using a movableelement (4) within said measuring vessel (7) to apply a restrainingforce (12) to said superabsorbent material (9) and capturing theexpansion of said superabsorbent material (9) within chambers (14) in acontinuous manner by optically capturing the change in height of pistons(4) which bound said chambers (14), traveling in a guide (7) and markedwith a height scale (6), in front of a background area (1, 27) fordetermining swelling kinetics curves.
 2. The method of claim 1, whereinthe height said piston (4) rises is captured optically by means of abackground area (1, 27) providing a contrast to said height scale (6) onsaid piston (4).
 3. The method of claim 1, wherein the pixel coordinatewhich corresponds to the tip of said height scale (6) on said piston (4)is convertible into a swell height of said superabsorbent material (9)via calibration.
 4. The method of claim 1, wherein said restrainingforce (12) acting on said superabsorbent material (9) is adjustable bythe dimensioning of said piston (4).
 5. The method of claim 1, whereinparticulate superabsorbent material (9) in particle sizes of from 100 μmto 1 mm is held in said measuring vessel (7) and is in contact with asolution (17) via a sieve fabric (13).
 6. The method of claim 1, whereinparticulate superabsorbent material (9) in particle sizes of from 400 μmto 700 μm is held in said measuring vessel (7) and is in contact with asolution (17) via a sieve fabric (13).
 7. The method of claim 1, whereinsaid determination of said swelling kinetics of said superabsorbentmaterial (9) accommodated in said chamber (14) of said measuring vessel(7) is effected by continuous contactless measurements over a time spanΔt (16) over which swelling kinetics curves (25, 26) are generatedagainst a constrasting background (1, 27).
 8. The method of claim 1,wherein said contactless capturing of said height of rise of said scale(6) on said piston (4) is effected concurrently on a multiplicity (29.1to 29.12) of parallel-connected measuring vessels (7) which dip into aconjoint reservoir (28) and are synchronously engageable to a solution(17) via said conjoint reservoir (28).
 9. The method of claim 8, whereinsaid capturing of said heights of rise of said pistons (4) is effectedagainst a background area (27) which extends across the width of allscales (6) on said multiplicity (29.1 to 29.12) of said pistons (4). 10.The method of claim 8, wherein said multiplicity (29.1 to 29.12) of saidmeasuring vessels (7) is disposed side by side and/or one behind theother and/or wholly or partly one on top of the other.
 11. The method ofclaim 1, wherein said contactless capturing of said height of 25 rise ofsaid scale (6) on said multiplicity (29.1 to 29.12) of pistons (4) iseffected in staggered measuring planes (32, 33, 34, 35) by an opticalsystem (20).
 12. The method of claim 1, wherein said piston (4) in saidmeasuring vessel (7) generates a pressure >50 Pa on said superabsorbentmaterial (9).
 13. The method of claim 1, wherein said optical system(20) continuously captures said heights of rise of said scale (6) onsaid pistons (4) against said contrasting background area (1, 27) as afunction of time and the captured values are fed to an automaticcomputer-controlled further processing system below said movablydisposed optical system (20).
 14. Apparatus for determining theswellability of superabsorbent material (9) such as polymer gels, forexample according to the method of claim 1, which comprises introducinga defined volume of the dry superabsorbent material (9) into a measuringvessel (7), using a movable element (4) within said measuring vessel (7)to apply a restraining force (12) on said superabsorbent material (9),wherein said superabsorbent material (9) is accommodated in a chamber(14) which is bounded by said measuring vessel (7) and by a movablepiston (4) therein, which are both constructed in metal, and saidchamber (14) is in constant communication with a solution (17) through asieve (13) and a frit (16).
 15. The apparatus of claim 14, wherein saidmovable piston (4) is provided with a scale (6) in the region of itsupper end face (5).
 16. The apparatus of claim 14, wherein saidmeasuring vessels (7) are disposed in a multiplicity (29.1 to 29.12) infront of a conjoint background area (27).
 17. The apparatus of claim 16,wherein the multiplicity (29.1 to 29.12) of measuring vessels (7) dipsinto a conjoint reservoir (28).
 18. The apparatus of claim 14, wherein amultiplicity (29.1 to 29.12) of measuring vessels (7) disposed instaggered measuring planes (32, 33, 34, 35) and comprising movablepistons (4) for determining the heights of rise are assigned backgroundareas (27) which each contrast the measuring planes (32, 33, 34, 35) andare scanned by a movable optical system (20).